DESCRIPTION: HIV-associated neurocognitive disorders (HAND), varying in severity from an asymptomatic to mild neurocognitive impairment to in its most serious form a debilitating dementia, develop in a subset of individuals infected with HIV-1. HAND results from an indirect neurotoxicity, as HIV infects macrophages and microglia, but not neurons, in the brain. The molecular mechanisms underlying neurotoxicity by HIV-1 infection in the brain are still largely unknown. Our studies and those of others have discovered a class of regulatory RNAs, microRNAs (miRNA) that are dysregulated in HIV-1 associated neurological disease. Recent findings indicate that miRNAs can be carried in extracellular vesicles such as exosomes, which have lately emerged as important mediators of cell-to-cell communication in the brain. Exosomes can release their cargo into target cells and trigger downstream signaling pathways. We are particularly interested in understanding the effect of such exosome-carried miRNAs on neurons. In particular, we will study miR-21. We have previously identified that miR-21 is significantly upregulated during SIV/HIV infection in the brain. We now find it is present within macrophages in the infected brain, and our in vitro studies reveal both human and mouse macrophages release miR-21 in exosomes. These miRNAs had a G/U rich region, capable of activating TLR7/TLR8. We believe that miR-21 and similar miRNAs are potential neurotoxic factors and are specifically released during HIV-1 induced insult to the brain. Here we hypothesize to study exosomal miR-21 and its effect on neurons in SIV/HIV-1 infection. These studies will be done in two specific aims; (1) In specific aim 1 we will utilize a robust strategy o isolate exosomes form SIV and HIV-1 infected brain tissue, characterize them, and determine SIV/HIV induced alterations in exosomal miR-21. (2) Specific aim 2 is specifically designed identify induction of neuro-injurious molecular signaling pathways during SIV/HIV-1 infection by exosomal miR-21. We will examine whether exosomal miR-21 activates toll like receptors and which downstream signaling pathways can harm neuronal health. These experiments will expand our knowledge on understanding the mechanisms accounting for the exacerbated neuronal damage during HIV-infection of the brain and therefore build a strong ground to build further therapeutic studies for the prevention of long-term neuronal damage in HAND.